1. Field of the Invention
The present invention relates to a combustion gas burner enabling a multi-stage control, and more particularly, to a combustion gas burner enabling a multi-stage control in which a number of premixed combustion gas burners each having an identical burner output capacity, are disposed in parallel with one another and a number of operating burners are varied according to a desired calorie or heat capacity.
2. Description of the Related Art
As is well-known, a boiler for heating and supplying hot water for use in a general home is divided into an oil boiler and a gas boiler according to a fuel used. The oil boiler or the gas boiler uses a burner for burning oil or gas which is used in the boiler.
Thus, a general burner obtains heat by burning fuel safely and efficiently. According to the kind of fuel used, the burner is classified as either a gas burner for combustion of gas, an oil burner for combustion of liquid fuel such as kerosene or diesel oil, or a powdered coal burner for combustion of coal.
Additionally, the burner is divided into a premixed combustion burner and a diffusion combustion burner according to a method for mixing fuel and air. The premixed combustion burner burns fuel and air which have been mixed in advance. The diffusion combustion burner burns mixed fuel and air, the fuel and air are separately supplied to a burner and mixed therein.
Most gas burners widely used as a home gas boiler chiefly adopts the Bunsen gas burner, a diffusion combustion gas burner. The Bunsen gas burner is chiefly used since air can be speedily supplied to heighten the temperature of flames. Thus, the temperature can be raised instantaneously and speedily.
As described above, most gas burners widely used for gas burner equipment such as a home gas boiler employ a Bunsen gas burner. This is because the Bunsen gas burner has a stable flame, thus there is a lower risk of backfire.
However, the Bunsen gas burner has a long flame and a high flame temperature, thus needs more that an theoretical amount of air. Accordingly, there is an increase loss of heat due to high-temperature exhaust gas. This leads to an increased amount of pollutants such as NOx and CO. As a result, the Bunsen gas burner is somewhat limited in accomplishing maximum efficiency and reduction of pollutants in the gas burner equipment.
The Bunsen gas burner includes a main burner which oversupplies gas and an auxiliary burner which oversupplies air. These are required to easily heighten an instantaneous temperature. Accordingly, the Bunsen gas burner can adjust the intensity and length of the flame.
In the Bunsen gas burner, the main burner is set so that an air surplus ratio is greater than 1.2. The auxiliary burner is set so that an air surplus ratio is smaller than 0.8. In this case, nitrogen oxide of 40 through 60 ppm is discharged, in comparison with the case that nitrogen oxide (NOx) of 120 ppm or so is discharged when the Bunsen gas burner is operated for combustion at a constant air-to-fuel ratio.
Referring not to FIG. 1, a perspective view showing a state of using a conventional Bunsen gas burner is shown. As shown in FIG. 1, the Bunsen gas burner 50 performs a combustion process as follows. Gas is primarily mixed with air 46 supplied by an air blower 42 and the mixture of the gas and air is burned in a combustion unit 45. To assist the combustion unit 45 in performing a combustion process, air 47 is secondarily inhaled into the combustion unit 45 to thereby cause a spread combustion process.
In the case of the spread combustion, the amount of oxygen is lacking and amount of gas is in surplus at the center of the flame. The amount of gas is lacking and oxygen is in surplus at the edge of the flame. Thus, gas and fuel are continuously spread toward the middle portion of the flame according to the difference of in concentration between gas and oxygen. Thus, keeping the fuel and gas burning. Also, part of the carbon monoxide produced at the center of the flame is discharged unless carbon monoxide is oxidized into carbon dioxide during a spread combustion process.
Referring now to FIG. 2, a perspective view showing a conventional Bunsen gas burner is shown. As shown in FIG. 2, the conventional Bunsen gas burner includes a combustion unit in which a plurality of Bunsen burners 10 are arranged in an array with a predetermined distance between them.
Each of the Bunsen burners 10 include an elongate main fire hole unit 11 which is formed of a group of slits which are installed in parallel with each other in the upper portion of the Bunsen gas burner. Also, the Bunsen gas burner 10 includes a flat main burner 1 where an intake hole 12 for inhaling a gas mixture is arranged laterally, and an auxiliary burner 2 where an auxiliary fire hole unit 13 is formed at either side of the main fire hole unit 11 over the whole width of the main fire hole unit 11. Simultaneously a common air intake unit 14 for inhaling a gas mixture is arranged laterally.
In addition, the main burner 1 is formed by pressing on the center position of a metal plate with a group of slits arranged in parallel with each other, forming the main fire hole unit 11, in which an expansion unit 15 is expanded and protruded with respect to the outer side of the main burner, symmetrically with a perpendicular surface including the central line.
Also, an intake hole 12 of inhaling fuel gas and primary air is installed in one side of the expansion unit 15, and a gas flow path 16 connected to the main fire hole unit 11 from the intake hole 12 is formed inside. Also, a cover 4 additionally equipped with a window 3 formed by extending the outer circumferential surface of the auxiliary burner 2 in a cross-linked from, is disposed at the main fire hole unit 11 and the auxiliary fire hole unit 13.
Meanwhile, the window 3 includes a plurality of rectangular windows 17 which open the upper portions of a group of sub-sets of four slits forming the main fire hole unit 11. The window 3 also includes an array of flame holes 18 of a slit shape which partitions the auxiliary fire hole unit 13 with a plurality of flame holes respectively and closes the auxiliary fire hole unit 13 partially.
However, in the case of the conventional Bunsen gas burner, gas sprayed from nozzles 6 in a gas supply tube 5 is supplied to the main burner 1 and the auxiliary burner 2 via the gas flow path 16 of the burner together with the primary air by a sprayed pressure. This is burnt in the upper portions of the main burner 1 and the auxiliary burner 2 to form flames through the main fire hole unit 11 and the auxiliary fire hole unit 13.
Since a plurality of the Bunsen gas burners 10 are connected in a line to form a burner assembly, the overall length of flame is long and the overall temperature of flame is high, thereby increasing a load with respect to an identical area. Further, since gas is burnt via the main fire hole unit 11 in the main burner 1 and the auxiliary fire hole unit 13 in the auxiliary burner 2, an air supply ratio is not controlled sufficiently. Thus, the amount of by-products such as carbon monoxide and nitrogen oxide discharged increases relatively in comparison with the premixed combustion gas burner, which causes an environmental pollution.
In particular, in the case where an existing Bunsen gas burner using a number of Bunsen gas burners 10 in combination for the purpose of high-load combustion, the number of burners becomes large. As a result, it is difficult to control combustion of each burner and the whole size of the burner assembly becomes large.
Meanwhile, a premixed combustion gas burner using knitted metal fiber mat of porous metal fiber weaving tissue as a surface material of a combustion gas burner functions to both reduce polluted materials, such as NOx and CO, and flame temperature. The knitted metal fiber mat of porous metal fiber weaving tissue, used as a surface material of a combustion gas burner, is woven like a fiber tissue with a metallic material of 50 μm or less in diameter . This is used as the surface material of the combustion gas burner to both perform perfect combustion of inflammable premixed gas on the combustion surface, and then heat the combustion surface of the gas burner formed of the knitted metal fiber mat of the metal fiber weaving tissue. The combustion heat thereby obtains strong and uniform solid-state radiation energy from the combustion surface of the gas burner.
Additionally, a loss of heat due to exhaust gas is reduced by reducing the amount of excessive air for combustion and lowering the temperature of combustion exhaust gas. This increases thermal efficiency and suppresses polluted materials such as NOx and CO to be discharged.
Also, a range of a combustion load (a turndown ratio: TDR) is considerably wider than that of the general gas burners whose TDR is 5 to 1. Additionally, the stability of the flame is remarkably superior to that of the general gas burner and employs a simple structure. As described above, the knitted metal fiber mat of porous metal fiber weaving tissue is widely used as a combustion surface material for a gas burner for home use, commercial use and industrial use to enhance thermal efficiency and lower polluted materials in gas combustion equipment.
In particular, materials such as ceramic or stainless steel, and knitted metal fiber mat of porous metal fiber weaving tissue are used as a combustion surface material for a gas burner. Since the knitted metal fiber mat of porous metal fiber weaving tissue has a thermal treatment effect which lowers the temperature of the rear surface of the burner to a value equal to or less than ignition temperature, it is known as a safe material for use with burner flames. This is do to the lower risk of backfiring through small holes on the knitted metal fiber mat of porous metal fiber weaving tissue when the knitted metal fiber mat is used as the combustion surface material of the gas burner in order to perform combustion of the premixed gas.
Also, the gas burner using knitted metal fiber mat of porous metal fiber weaving tissue has an advantage of having no need to specially countermeasure a backfire phenomenon, which is used to reduce polluted materials such as NOx and CO and lower the temperature of flames.
However, in the case that the temperature of flames is low in the conventional premixed combustion gas burner, the burner flames may be unstable. This can lead to increased production cost, and it may be difficult to fabricate it. Also, it may be more difficult to stably control combustion of the premixed gas in home gas burner equipment, which has a simple structure design.
Also, in the case that ceramic, stainless steel, or knitted metal fiber mat of porous metal fiber weaving tissue is used as a combustion surface material of the premixed combustion gas slits, a premixer for premixing fuel gas and air may become large and somewhat complicated. As a result, air blowing resistance increases due to a loss of pressure in the premixer. This may lead to abnormal noise at part of a high-load region during combustion or main flames of the gas burner may be unstable.
As described above, if a mixing chamber which is an additional unit for mixing fuel gas and air and supplying the mixture is used in the conventional premixed combustion gas burner, the structure becomes complicated and it is difficult to set a mixing ratio of fuel gas and air into an appropriate value.
In particular, it is impossible to apply the mixing chamber to a burner performing a multi-stage control.